The long range objective is to understand the molecular and structural basis of cytoplasmic streaming and cell contractility. We are pursuing a calcium sensitive fraction from Physarum to determine the basis for the sensitivity and to see if it is related to the actomyosin system known to exist in this organism. We have discovered that 5'AMP will induce filament formation in high speed extracts of Physarum and are studying the mechanism of this effect. We are endeavoring to show that some calcium sensitivity results are due to the weak binding of a pyrophosphohydrolase to the actomyosin complex.